The volume of calls in a telephony network significantly varies over time, and traditionally, such networks have been engineered to support peak traffic levels associated with social or business calling patterns. There are, however, certain events that will generate traffic patterns that exceed the supported peak levels. Examples of such events include mass calling events triggered by promotional or advertising campaigns, catastrophic events including natural disasters and acts of war, and denial of service attacks in packet-based networks. Further, equipment failures, such as telephony switch malfunctions, may also lead to situations where call volumes exceed network capacity. Left unchecked, such situations may disable network equipment and significantly impact the throughput of the entire network.
The role of network session controls is to localize the effect of unexpectedly high traffic levels or malicious session requests, and to maintain the agreed service levels for subscribers. While individual telephony switches in a circuit-switched network may implement nodal session control mechanisms, the network session controls help to isolate the source of undesired session requests and minimize the impact on other calls. Traditionally, network call or session controls for overload situations have been addressed in circuit-switched networks using two mechanisms intended to throttle or otherwise reduce the call volume arriving at a given switch. The first mechanism incorporates trunk group management, which dynamically reduces the number of trunks available between switches during overload situations. The second mechanism provides screening in service transfer points (STPs) in the call signaling network to effectively filter call setup requests based on point codes, calling number, called number, and the like.
Unfortunately, neither of the mechanisms used in the circuit-switched network are available for packet networks, since packet-based soft switches do not have the concept of trunk groups, and there are no STPs. Due to their open nature, packet networks are more vulnerable to malicious attacks executed under the guise of session initiation or establishment. The only session or overload control solutions for packet networks include discarding incoming messages or responding to session request messages with a message indicating that service is unavailable. In the former case, discarding incoming messages affects not only new session initiation attempts, but also sessions that are already established. Responding to session request messages with service unavailable messages requires additional processing from the overloaded element, and doesn't provide any remedial actions to other nodes or elements in the network. Accordingly, there is a need to develop a protection mechanism that allows service providers to limit or prevent certain session requests from being propagated throughout a packet network in an efficient manner.